Refrigerating cycle is composed of a compressor, a condenser, an evaporator, an expansion valve, a dryer, an oil separator, a liquid separator, and so forth. Based on the 2nd law of thermodynamics, the refrigerator absorbs heat from the low heat supply and emits it to the high heat supply with the assistance of the compressor's work. Refrigerant used in the refrigeration cycle absorbs the heat from the surrounding and evaporates in the evaporator under low temperature. In the compressor, the refrigerant is compressed to the gas having high temperature and high pressure and then, it is cooling again in the condenser and the phase thereof is changed to the liquid having high pressure. Finally, the pressure thereof is decreased to the initial value on passing through the expansion valve. During these cycles, the heat is transferred from the low heat supply, i.e., surrounding to the high heat supply and the refrigerant performs continuous cooling of the surrounding.
According to operation temperature, the refrigerant is classified into 3 classes: a refrigerant for low back pressure condition, a refrigerant for high back pressure condition, and a refrigerant for middle back pressure condition. The refrigerant for low back pressure condition operates at a temperature of −35-−15° C. The refrigerant for middle back pressure condition and the refrigerant for high back pressure condition are −15-+5° C. and −10-+10° C., respectively. As a representative example of the refrigerant for high back pressure condition, HCFC-22 (simply, R-22), one of HCFC (Hydrochlorofluorocarbon) refrigerant, can be mentioned. Due to its excellent thermodynamic properties, HCFC-22 has being widely used in refrigerators such as household and industrial air-conditioner. However, the use thereof is strictly restricted for being an environmentally hazardous material having high ozone layer destroy potential (ODP=0.05) and global warming potential (GWP=1500).
For these reasons, the development of HCFC-22 substitution refrigerants has been continuously progressed. R-502, which is a mixture of CFC (chlorofluorocarbon) refrigerants, R-407C and R410A, which are mixtures of HFC (hydrofluorocarbon) refrigerants, and R290, which is HC (Hydrocarbon) refrigerant, were suggested as substitution refrigerants for HCFC-22.
R-502 is an azeotropic mixture of CHF2Cl and CF2ClCF3, which is a mixture of two refrigerants but acts as a single refrigerant, but there are questions as to the environmental safety such that the use thereof is strictly restricted.
R-407 is a non-azeotropic mixture of three refrigerants, R-32(CH2F2)/R-125 (C2HF5)/R-134a(CF3CH2F) in which the ratio of the refrigerants is 23/25/52 wt % and its volumetric cooling capacity is almost equal to that of HCFC-22. However, this refrigerant composition is suffered from the disadvantages that it has 8.1% higher condensing and evaporating pressure than HCFC-22 and the coefficient of performance thereof is lower than HCFC-22. In addition, because of its non-azeotropic characteristic, about 4-5° C. of the temperature grade is occurred during the evaporating and condensing process. Due to phase change of the refrigerator, this results performance deviation even the same amount of the refrigerant is introduced into a refrigerator. Further, Because of its poor compatibility with a refrigerating oil, special oils like ester oils or poly alkylene glycol (PAG) oils are necessarily required rather than mineral oils. However, the ester oils or PAG oils may cause significant damages to a refrigerator by the absorption of moisture when they are exposed to the air. For these reasons, they cannot be directly dropped in the refrigerator systems adopting HCFC-22 refrigerant. That is, systemic changes of the conventional refrigerator such as a compressor and the manufacturing equipments are necessarily required. Also, this refrigerant composition is not environment-friendly. Specifically, the global warming potential (GWP) of R-407 is about 1530 (CO2=1, 100 yr), which is very high.
R-401A which is a mixture of 50 wt % of R-32 (CH2F2) and 50 wt % of R-125 (C2HF5) is an azeotropic mixture in which temperature grade does not occur during evaporation and condensation. This refrigerant composition has higher volumetric cooling capacity than HCFC-22. However, the composition cannot be directly dropped in the conventional refrigerator systems adopting HCFC-22 refrigerant without any systemic changes or modifications, because the condensing and evaporating pressures are 56% higher than that of HCFC-22. Further, the composition also suffers from disadvantages that special oils like ester oils or poly alkylene glycol (PAG) oils are necessarily required rather than mineral oils and the global warming potential (GWP) thereof is about 1730 such that it is not environment-friendly.
R-290 that is a hydrocarbon refrigerant has been actively researched as a substitution refrigerant for the HCFC-22, because of its excellent thermodynamic properties and low global warming potential, specifically 3 (CO2=1, 100 yr). Despite of its excellent thermodynamic properties, it suffers from disadvantages that it requires systemic changes or modifications on refrigerator systems such as a compressor because of its high volumetric cooling capacity. Further, it may also be susceptible to flammability and explosiveness. In addition, Non-azeotropic refrigerant of propane and pentafluoroethane (C2HF5) having high volumetric cooling capacity cannot be directly dropped in the conventional refrigerator because it has much higher vapor pressure than HCFC-22. 2-3° C. of temperature grade occurs during condensing and evaporating processes. That is, neither R-290 nor Non-azeotropic refrigerant of propane and pentafluoroethane (C2HF5) is applied to the conventional refrigerator systems without any systemic changes.
Meanwhile, U.S. Pat. No. 5,624,595 disclosed a refrigerant composition comprising silicone oil as an additive in order to improve flammability of the refrigerant. However, the amount of silicone oil added is strictly restricted because it circles through the refrigerating cycle as liquid state and reduces the cooling capacity and accumulation thereof in the evaporator may cause significant damages to the refrigerator. Further, since it is separated from the refrigerant while it is stored for a long time after being manufactured, the improvement in flammability is relatively high when the real refrigerant is discharged as a gas from the vessel.
As a result, in order to use the refrigerants suggested in the above, systemic changes or modifications of the refrigerator systems adopting HCFC-22 refrigerant is necessarily required for the reason that they have different properties than HCFC-22 This systemic changes waste enormous cost and resources and the cost required for modifying manufacturing equipments is incalculably high.
Therefore, it has been demanded to develop new azeotropic refrigerant, which could be directly dropped in the conventional refrigerator systems in which HCFC-22 was used as a refrigerant such that systemic changes can be minimized, which has excellent volumetric cooling capacity, high performance coefficient, and evaporating pressure feature without showing temperature grade during evaporating and condensing processes, and which is compatible with components of the refrigerator system such as refrigerating oil.